Effects of chronic doses of ozone on field-grown loblolly pine: seedling responses in the first year

A study was designed to examine responses of loblolly pine (Pinus taeda) to chronic exposure to ozone (O 3 ) in the field. Seedlings of four full-sib families of loblolly pine were planted in a field near Raleigh, NC, and exposed daily (May 27 to October 24, 1985) in open-top chambers to O 3 ranging from 0.5 to 1.96 times the O 3 concentration in non-filtered (NF) air. One-fourth of the plants in each plot were removed during each of two harvests (August and October) to measure effects of O 3 on plant growth. Plants of each family exhibited foliar symptoms characteristic of O3 injury after five months of exposure to any greater-than-ambient O 3 concentration, and one family exhibited symptoms after five months of exposure to NF air. Ozone dose-plant response relationships were quantified by regression for stem height, stem diameter, biomass, and other plant morphological and yield characteristics. All relationships were linear for three families, but one family exhibited no significant growth response relationship of O 3 dose. Dose-response equations suggest a maximum growth suppression of 10 percent for NF air compared to charcoal-filtered air (i.e., 0.5 × NF) in the first season of exposure.